NEW Electrostatic headphone amp

Doc B. · 6813

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Offline Pflugshaupt

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Reply #30 on: June 09, 2020, 07:11:51 AM
Can it drive the notoriously hard to drive Stax 007 (mk1)?
« Last Edit: June 09, 2020, 08:15:52 AM by Pflugshaupt »



Offline Paul Birkeland

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Reply #31 on: June 09, 2020, 08:32:00 AM
The SR-007 says 100dB for 100V RMS.  This amp can do close to 600V peak to peak, which is over 200V RMS, so yes, output shouldn't be a problem.  The amp would be down a dB or two at 20kHz on the SR-007.

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Pflugshaupt

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Reply #32 on: June 09, 2020, 11:59:00 AM
As far as I know (and with the risk of making a fool of myself as this is just collected internet knowledge) the issue some amps have with the SR-007 isn't just voltage swing, but how much current they deliver. I am currently running a modified Stax T1 hybrid amp to which I added constant current sources, so there could be more current going to the headphones instead of being burnt by resistors. If there isn't enough current, the headphones cannot produce their low end properly which goes amazingly deep. The author of the mod wrote that the modded amp can deliver up to 9.2 mA to the headphones (instead of max. 3mA in stock config), but from owners of custom energizers values up to 20mA are stated to improve the sound.



Offline Paul Birkeland

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Reply #33 on: June 09, 2020, 07:07:32 PM
That is an odd sentiment that there's a lot of current required to drive an electrostatic headphone at low frequencies.  They are a capacitive load, and the SR-007 will load an amp at 20Hz about as much as an 82 million ohm resistor.  I'm having trouble counting all the zeroes, but I think that's 7 micro amps of peak current at 600V peak to peak drive.

I do agree that only having 3mA of operating current is not nearly enough for any electrostatic headphone, and would indeed give a thin, rolled off sound.  I run 10mA of current in the output stage per channel, which strikes a balance between keeping the plate load resistors reasonably high, overall dissipation in the output tubes and loading resistors reasonable, but also extracting solid performance. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Pflugshaupt

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Reply #34 on: June 09, 2020, 11:24:07 PM
Thanks for your replies. So I guess I got confused about the low end. All I can say is that the CCS mod really made the SR-007 sound a lot better on that Stax T1. I'm sure owners of the high-end staxes will be happy to hear about these 10 mA. Stax' own tube amps have a bad reputation for not delivering enough power that might spill to all tube amps.

If you had the kit, I'd buy it now. Unfortunately my wallet says no to a pre-built one. Plus I love the building at least as much as the listening. Should you end up creating a kit, I'd volunteer to buy and build one of the first ones and give detailed feedback about the instructions.



Offline Paul Birkeland

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Reply #35 on: June 10, 2020, 07:01:52 AM
The kit price would end up being not all that much lower than the finished unit. 

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Pflugshaupt

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Reply #36 on: June 10, 2020, 08:54:50 AM
Ok you got me. And I like green.



Offline adydula

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Reply #37 on: August 05, 2020, 04:07:34 AM
Wow!!

Havent heard VTVM in a long time!!

One of the questions I used to ask prospective electronics tech hires for IBM "back in the day" was "What the difference between a VTVM and a VOM"??

:>)

Alex



Offline Paul Birkeland

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Reply #38 on: August 05, 2020, 05:17:58 AM
"What the difference between a VTVM and a VOM"??

Vacuum Tube Valley Magazine and Voice of Music? ;) 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline adydula

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Reply #39 on: August 05, 2020, 05:39:55 AM
Wow....YOU GOT IT RIGHT!!!

 ;)



Offline nzastro

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Reply #40 on: September 08, 2020, 11:06:53 PM
Hi all,
Just registered with Bottlehead.
I'm living in New Zealand and am looking for an electrostatic amplifier for my old Stax SR-5 Gold.
I'd need a complete kit as parts are difficult and expensive to source here in New Zealand.
Any help would be much appreciated.
Thank you!
Regards, Tony.



Offline Paul Birkeland

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Reply #41 on: September 09, 2020, 04:45:50 AM
I'm happy to make you an amp and send it down there.  We decided not to go down the kit road, as these aren't all that easy to debug and really need to be buttoned up in a metal box.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Doc B.

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Reply #42 on: September 09, 2020, 02:20:11 PM
This is PB's latest completion, in red wrinkle finish.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.


Offline Doc B.

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Reply #43 on: September 13, 2020, 10:44:38 AM

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.